I. Field of the Invention
This invention relates to a fractional horsepower electric motor assembly and, in particular, to a centrifugal governor mounted to the rotor shaft of the motor and positionally maintained by the terminal board associated with the components of the assembly.
II. Description of the Prior Art
Control components for electric motors vary widely in their structure and operation. Generally, these components are adapted for safe and efficient operation of the associated motor including shutoff of one of a plurality of windings of the motor when a predetermined rotational value is attained. Centrifugal governors utilize the radially outward inertia generated by rotation of the rotor shaft to engage and disengage an electrical switch. A pendulum weight may be utilized to make the governor more sensitive or to overcome other forces associated with the governor assembly. Such forces may include an extended spring designed to bias the pendulum towards its at rest position or mechanical levers which also move the weighted member towards the at rest position. However, many of these past known assemblies have been found to be unduly complicated resulting in failure of the switch and adding to the weight of the motor. In particular, the use of extension springs to bias the pendulum results in stretching of the spring over prolonged use which retards the sensitivity of the mechanism. Moreover, mechanical levers are subject to sticking and failure which can result in damage to the motor assembly. Frictional wear may also reduce the effectiveness of the governor switch.
The sensitivity to which the switch reacts to small changes in the rotational speed of the motor can be critical. Centrifugal switches which utilize a flyweight mass disposed close to the rotary axis of the shaft can be slow in reacting because the flyweight requires larger changes in rotation to be affected Furthermore, many pendulum weighted switches and extension spring switches can react to turbulence applied to the motor assembly. Such past known switches do not readily absorb such shocks.
The governor switch and its associated components are normally housed within the end bell of the motor housing and secured by individual mounting hardware. Thus, if a component fails the governor, switch, capacitor and/or terminal board must be laboriously disassembled for replacement. In addition to significantly increasing assembly and repair costs, the additional mounting hardware can add to the weight and size of the motor assembly. Moreover, regulatory requirements can also increase the size of the motor housing by requiring that any vent openings be positioned such that fluid splash will not reach the inner windings of the motor. This can require that the housing be unnecessarily long in order to properly position the vent openings.